1. Field of the Invention
The present invention relates generally to lids for airtight containers and, more particularly, to a lid for an airtight container which is configured such that the impact generated when locking the lid to the container body is minimized, thus improving the durability of the lid, and such that the smooth flow of raw material is ensured when forming the lid, thus preventing production defects.
2. Description of the Related Art
As well known to those skilled in the art, airtight containers contain and store food therein. Such an airtight container includes a container body, which is open on the upper end thereof to contain food therein, and a lid, which seals the open upper end of the container body.
FIGS. 1A and 1B are enlarged sectional views showing critical parts of a container body 10 and a lid 20 to illustrate the coupling therebetween, according to a representative example of the conventional technique. As shown in the drawings, a sealing member 30 is interposed between the container body 10 and the lid 20 to airtightly seal the container body. Furthermore, a locking depression 11 is formed in the outer edge of the open upper end of the container body 10. Locking flap handles 21, each of which has a locking protrusion 22 to be locked to the locking depression 11 of the container body 10, are rotatably connected to the outer surface of a rim part of the lid 20 by a film hinge 23. The film hinge 23 is connected to a gusset part 24, which protrudes outwards from the outer surface of the rim part of the lid 20, such that the locking flap handle 21 is rotatable upwards or downwards.
As shown in FIG. 1A, in the state in which the lid 20 is placed on the container body 10, the locking flap handles 21 are rotated downwards (in the direction designated by the arrow) around the respective film hinges 23. Then, the locking protrusion 22 of each locking flap handle 21 is locked to the locking depression 11. Thereby, as shown in FIG. 1B, the container body 10 is airtightly sealed.
However, the conventional airtight container having the above-mentioned construction has the following several problems.
First, synthetic resin or glass is typically used as raw material for the conventional container body 10. In the case of such material, due to a thermal change in the state between molecules, a contraction phenomenon, by which the dimensions of the container body 10 are reduced and the shape of the container body 10 thus varies, is induced. Hence, the dimensions of the manufactured container bodies 10 may become different from each other.
In other words, as shown in FIG. 1A, the length l between the open upper end of the container body 10 and the locking depression 11 may vary depending on a contraction rate of the manufactured container body 10. The length l may exceed a desired tolerance range.
Here, in the case where the length l is relatively short, because the lid 20 has the sealing member 30, which is elastically changed in shape within a predetermined range, there is no difficulty in covering and sealing the container body 10 without applying an excessive load to the film hinge 23. However, in the case where the length l is relatively long, when the locking protrusion 22 is locked to the locking groove 11, a relatively large load is applied to the film hinge 23, thus increasing creep. Thereby, impact occurring at the time of locking is concentrated on the film hinge 23. As a result, a crack may occur in the film hinge 23, with the result that the film hinge 23 tears.
In brief, as shown in FIGS. 1A and 1B, the film hinge 23 is very thin compared to the gusset part 24 or the locking flap handle 21. Typically, the film hinge 23 is about 0.3 mm thick, in consideration of the rotation of the locking flap handle, locking and unlocking operations thereof, and shear fracture thereof. Therefore, in the case where the length l is relatively long, impact is concentrated on the film hinge 23, which is relatively thin. As a result, the film hinge 23 may be damaged, particularly, easily tear.
Second, in the case of the lid 20 made of synthetic resin, in a portion of a mold for forming the film hinge 23 of the lid 20, which is relatively thin and thus forms a stepped portion on the outer edge of the lid 20, the smooth flow of raw material is not ensured. Hence, there is a problem in that a defective forming phenomenon, such as an unforming or albinic phenomenon, may occur in the event that material is insufficiently charged into the portion of the mold corresponding to the film hinge 23 when forming the lid 20.
Third, in the conventional technique, because the film hinge 23 is connected to the gusset part 24, which protrudes outwards from the outer surface of the rim part of the lid 20, when the locking protrusion 22 is locked to the locking depression 11, a gap d is defined between the outer surface of the rim part of the lid and the inner surface of the locking flap handle 21, as shown in FIG. 1B. Therefore, creep is concentrated on the film hinge 23, so that there is a problem in that shear fracture of the film hinge 23 is promoted.